This invention relates to preventing cerumen, or ear wax, from interfering with the operation of sound transmission devices, especially "in the ear" hearing aids, and is particularly concerned with a novel filter for achieving that result.
The human outer ear comprises the visible external ear, or pinna, and a dynamic S-shaped canal that has a generally oval cross section and is about an inch (2.5 cm) long. Cerumen is secreted by the walls of the canal in the outer half inch (1.2 cm) or so and gradually moved outward; some believe that this outward movement is brought about by cilia in the walls, but more likely it is caused by the natural action of the ear canal. When a hearing aid is inserted into the outer 1/4 inch (about 0.6 cm) of the canal, it becomes susceptible to cerumen, which mixes with sloughed off skin and often fouls the hearing aid's sound delivery tube, thereby reducing its efficiency.
When the sound delivery tube of a hearing aid clogs with cerumen and reduces the effectiveness of sound transmission, the wearer of a hearing aid typically turns up the volume control. This in turn results in two undesirable conditions. Not only does the hearing aid battery wear out more quickly with certain types of circuit, but the likelihood of embarrassing and frequently painful feedback howl also increases. Most importantly, cerumen in the sound tube of the hearing aid is the basis for large numbers of costly hearing aid repairs.
There have been numerous attempts to modify hearing aids to avoid the problems discussed in the preceding paragraphs. Thus, for example, U.S. Pat. Nos. 4,870,689 and 4,972,488 disclose a tubular passage having a series of baffles that define a "tortuous path" that the wax must travel before reaching the sound tube. U.S. Pat. No. 4,800,982 describes a hearing aid through which solvent may be pumped to remove wax buildup. U.S. Pat. No. 4,953,215 describes a hearing aid in which a domed membrane having a small central opening is provided, wax being said to accumulate in a ring around the base of the membrane.
Still others have attempted to devise some type of filter to prevent ear wax from reaching the sound delivery tube. For example, U.S. Pat. Nos. 3,414,685 and 4,984,277 discuss various prior art wax filters, noting the apparent difficulty in replacing them after they are soiled. In each case, the patentees' approach to the problem is to provide a one-piece plastic part that has numerous openings around the periphery and snaps around the sound delivery tube opening. A somewhat similar device is shown in U.S. Pat. No. 4,553,627, where a snap-on wax guard has a cross passage through its head that intersects an axial passage in its stem; ear wax is removed by pushing a tool through the cross passage. Still others have mechanically mounted screens or other filters beyond the sound delivery tube opening, but removal and replacement has been difficult, especially since persons wearing hearing aids are often advanced in years and unable either to see clearly enough or to perform fine physical actions well enough to replace the filters.